The present invention relates generally to halopolymer materials with adhesive surfaces, and more specifically, to protective appliquxc3xa9s as paint replacements for a wide range of substrates. The appliquxc3xa9s are layered structures, or polymeric films, generally halopolymers which have been modified by the introduction of surface hydrogen and oxygen or oxygen-containing functionalities. These reactive sites are suitable for chemically bonding with adhesive materials to form composite structures possessing superior peel strengths, resistance to delamination and protective properties when applied to surfaces, as replacements for the usual protective paint systems widely used in the aerospace, land and marine fields in general, and including the chemical, food processing and transportation industries. More particularly, the appliquxc3xa9s find numerous applications for aircraft and spacecraft parts and assemblies, partial and complete fuselage panels, wings for enhancing laminar flow, reducing ice formation and friction, entire aircraft hulls, aircraft markings and decals; replacements for paints, including architectural or as decorative appliquxc3xa9s suitable for printing, with emblems for use as transfer films and decals for rail cars, highway vehicles, including tractor-trailer rigs; protective films for marine vessels, and so on. The adhesive backed appliquxc3xa9s also have numerous utilities for internal surfaces, such as protective liners for containment vessels in the chemical and food processing industries, to name but a few.
Halopolymers are a group of polymers with carbon chains wherein all or a percentage of the carbons have covalently bonded halogen atoms. Halopolymers are characterized by extreme inertness, high thermal stability, hydrophobicity, low dielectric properties and low coefficients of friction. Representative examples of halopolymers that exhibit these characteristics include fluoropolymers and fluorochloropolymers, such as fluorohydrocarbon polymers, e.g., polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE), including the well known fluorocarbon polymers, e.g., perfluorinated polymers, like polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (ePTFE), FEP, perfluoroalkoxy polymer like PFA and MFA and copolymers and terpolymers thereof, for example, a terpolymer derived from TFE, hexafluoropropylene and vinylidene fluoride (THV), etc. However, because halopolymers are so inert and have low coefficients of friction, they will not reliably bond to other surfaces, or bond to value-added molecules. As such, the sought after characteristics of a halopolymer, such as inertness and hydrophobicity are not easily transferred to another substrate because of the difficulty in adhering a halopolymer film to the substrate.
Several attempts have been made to modify halopolymers to provide more bondable surfaces. For instance, U.S. Pat. No. 4,933,060 discloses a reactive gas plasma process wherein a glow discharge in an oxygen containing atmosphere leads to the formation of oxygen-containing functionalities on the surface. However, this method merely etches the surface creating transient oxygen-containing functionality, and the activity of the bonding sites is short-lived rendering an etched material with a limited shelf-life. Furthermore, the polymeric chains containing the oxidized surface functionalities undergo unavoidable reorientation due to their low molecular weights and subsequent migration, as described by H. Yasuda et. al. in J. Polym. Sci.: Polym. Phys. Ed., 19, 1285 (1981). As a result, surfaces of an etched halopolymer have limited periods of reactivity, and must be applied to an adhesive before reorientation of the etched surface. Moreover, bonds formed between the adhesive and etched halopolymer material lack permanency and tend to degrade under UV radiation, humidity and thermal stress conditions, due to rearrangement of the polymer. British Pat. Pub. 998,807 provides for a method of increasing adhesiveness of halopolymers using corona discharge plasma in an inert atmosphere which is essentially oxygen-free. However, the processed material must be maintained in an oxygen-free atmosphere to retain activity. Once the surface is exposed to moisture or oxygen the treated surface becomes deactivated limiting useful shelf-life. Furthermore, corona discharge plasmas are non-uniform plasmas generated from a point source, so the processed material is not uniformly modified or activated. The lack of uniformity of the surface disrupts continuity in batch production of the modified film.
A further method of modifying halopolymer materials to increase adhesiveness includes etching the halopolymer material by reacting with an alkali metal and naphthalene. However, this method provides a low level of defluorination. Consequently, the material readily degrades under thermal and ultraviolet stress conditions. Furthermore, the surface is chemically roughened (i.e., etched) which, in addition to an inconsistent degree of modification, provides nothing more than a non-permanent mechanical bond.
Fluoropolymers have also been suggested for use in the fabrication of paint replacement films, especially as corrosion protective surface coatings, for instance, in the form of appliquxc3xa9s. They have been of interest in both commercial avaition and for aerospace applications. Durable paint replacement films offer potential benefits of lower aircraft production costs, reduced maintenance requirements, weight reduction, environmental benefits, to name but a few.
One example of exterior protective appliquxc3xa9s intended as replacements for aviation paint systems for reduced lifecycle costs, improved performance and protection of surfaces from corrosion is disclosed by U.S. Pat. No. 6,177,189, to Rawlings et al. A paintless coating system is disclosed for replacing conventional paints on metal or composite aerospace parts and assemblies consisting of an appliquxc3xa9 having a topcoat or external film, a vapor barrier interfacing with and completely underlying the topcoat, and an adhesive on at least one face of the vapor barrier for adhering the appliquxc3xa9 to a surface of the part or assembly. More specifically, the topcoat consists of an organic resin matrix elastomeric composite, particularly a rain and thermal resistant fluoroelastomer. The intermediate vapor barrier which functions to eliminate active transport of water vapor or other corrosive agents to the substrate being coated, consists of a terpolymer derived from TFE, hexafluoropropylene and vinylidene fluoride. The preferred adhesive is a pressure sensitive acrylic. According to Rawlings et al the adhesive should hold the appliquxc3xa9s on the surface during normal operation, but should also be peelable without leaving a residue on the substrate for easier replacement.
While Rawlings et al reported that testing of their appliquxc3xa9s provided protection at 500 mph, comparable to special rain coatings in some conditions, they also observed delamination occurring in several test specimens between the topcoat film layer and the vapor barrier.
Accordingly, it would be highly desirable to have improved adherent protective halopolymeric surface coatings or appliquxc3xa9s as a paintless system of protective films for a wide range of end use applications for both interior and exterior surfaces, especially including aerospace, land and marine applications which not only provide the needed protective barrier against corrosion, but are also more fail safe in resisting delamination between the layers of the composite under the most severe operating conditions.
It is therefore an object of the present invention to provide surface modified halopolymers which repel water and other polar solvents, as well as non-polar solvents, possess high thermal stability, low friction coefficients and chemically bond to adhesive substances to form permanent bonds with superior strength.
It is a further object of this invention to provide adhesive-oxyhalopolymer composites comprising a modified halopolymer material having substituted functional groups that chemically bond to an adhesive material forming a bond that does not significantly degrade due to chemical attack, ultraviolet radiation, humidity, temperature extremes, salt, acid or caustic agents, steam and/or reorientation of substituted functional bonding sites.
Yet another object is to provide adhesive-oxyhalopolymer composites that can withstand attack by chemicals, ultraviolet radiation, humidity, temperature extremes, salt, acid or caustic agents and steam.
A further object of the invention is to provide a surface modified halopolymer film having two sides of which the first side is chemically bonded to an adhesive wherein during the wrapping or overlapping of the film, the adhesive coated first side can bond to the second side. One or both sides of the halopolymer film may be modified.
A still further object is to provide an adhesive-oxyhalopolymer composite wherein the oxyhalopolymer is uniformly treated and reproducible to provide quality control in the adhesive end product.
Yet another object is to provide methods for preparing adhesive-oxyhalopolymer composites having a modified surface which is not roughened or damaged by plasma etching, but instead at least one surface is controllably modified by the introduction of hydrogen and oxygen or oxygen-containing groups onto the surface matrix of the oxyhalopolymer to impart permanent chemical reactivity to the surface.
In this regard, it has been discovered that when the surface of a halopolymer material is exposed to radio frequency glow discharge (RFGD) in the presence of a hydrogen gas-vapor mixture comprising water, methanol, or other oxygen containing liquids (e.g., formaldehyde), a modified surface forms which comprises a controllably reduced amount of the original halogens, usually fluorine atoms, which are replaced with controlled amounts of hydrogen and oxygen or oxygen-containing groups covalently bonded to the carbon backbone of the polymer. The surface modified halopolymer material, which is an oxyhalopolymer, retains the unique properties of the original halogenated material, i.e. low surface energy. However, the surface modified halopolymer or oxyhalopolymer is also reactive and chemically bonds with an adhesive substance forming a stable and permanent bond with surprising and unexpected superior strength.
It is yet a further object of the invention to provide a novel class of surface protective coatings, mainly films and appliquxc3xa9s for use as paint replacements for bonding to a broad range of substrates, both interior and exterior surfaces, metallic, non-metallic, including polymeric and ceramic surfaces. The paint replacement films are especially useful in the aerospace field for application to exterior surfaces of aircraft and spacecraft, in aviation, providing protection for fuselage panels, wings as a paintless system for enhancing laminar flow, reducing friction and ice formation, hulls, aircraft/spacecraft markings and decals. The adhesive backed film composites and appliquxc3xa9s are also useful as paint replacements for marine vessels and shipping; land vehicles, such as highway trailers, railcars, protective liners for tank cars; liners for containment vessels and reactors in the chemical and food processing industries, and so on.
In addition to the halopolymers and fluoropolymers previously mentioned, the paint replacement films may also be fabricated with copolymers, terpolymers and polymeric blends. The halopolymers may also comprise various outer layers and coatings, including additives, such as carbon, metallic or metal oxide particles, in the form of flakes, fibers and pigments, for example, including constituents which impart thermal, optical, magnetic, electromagnetic, electronic and/or mechanical properties thereto.
The oxyhalopolymer materials of the invention may be in the form of a film, sheet, powder, bead, fiber, mesh, mold, coating, tubing, porous veiled material or any other shape utilized for a specific application. The modified film with oxyhalopolymer surface is readily chemically bonded to an adhesive. As previously mentioned, the appliquxc3xa9 comprising adhesive-oxyhalopolymer film composites of the invention may be applied to virtually any substrate, including medical devices, electrically conductive and nonconductive, metal, non-metal, wood, ceramic, glass, plastic, etc., to impart the desired protective properties of the halopolymeric material to the new surface, and any devices encapsulated in the appliquxc3xa9s. These adhesive-oxyhalopolymer film composites are useful for innumerable household, medical and industrial applications and can be applied to a substrate in situ, to preserve, protect and extend the life of the object. Such objects may include the bases of telephone poles, fence posts, concrete foundations, drain gutters, entire aircraft/spacecraft hulls, airplane wings for corrosion protection and to reduce ice formation and friction, hulls of ships and docks to prevent marine biofouling, fume hoods, machine tools, walls of buildings as anti-graffiti coatings, bondable gaskets, chemical containment vessels and pipes for protecting the containment structure, coil coatings, metals, such as carbon steel or any other surfaces which may be damaged or corroded by exposure to weather conditions, moisture, oceanic conditions water vapor, humidity, mildew, temperature, salt, corrosive chemicals, radiation, and so on.
In forming the adhesive-oxyhalopolymer composites an outer surface of a halopolymer is modified by substituting hydrogen and oxygen or oxygen-containing groups for at least a portion of the halogens atoms on the halopolymer surface. Subsequently, the oxygen or oxygen-containing groups on the surface of the modified oxyhalopolymer-containing material are reacted, i.e., chemically bonded to an adhesive to form the composite films of the present invention. The bulk characteristics, such as chemical resistance, inertness, stability of polymeric structure and hydrophobicity of the original starting halopolymer material are retained below the outer surface of the modified oxyhalopolymer.
Generally, the adhesives which may be applied and reacted with the oxyhalopolymer layer to form the composites and protective films and appliquxc3xa9s of this invention are homopolymers and copolymers of acrylates, acetates and mixtures thereof. Other representative examples of useful types of adhesives are polymers of cyanoacrylates, epoxies, sulfides, vinyl esters, e.g., polyethylene-vinylacetates and copolymers thereof; silicone-containing adhesives, e.g., polysilicones, polysiloxanes; rubber type adhesives, including fluoroelastomers; the urethanes, including the etherurethanes, unsaturated polyesters, and copolymers or blends of the above cited materials
Either contact, pressure sensitive, or thermoplastic based adhesives may be used. The adhesive systems of the invention may include certain additives, like corrosion inhibitors, crosslinking inhibitors, and various other materials, such as carbon, metals or metal oxide particles, flakes, fibers or others which can impart thermal, optical, magnetic, electromagnetic, electronic or mechanical properties, can be used.
The morphological properties of the oxyhalopolymer, at the molecular level, remain substantially unchanged from those of the starting halopolymer while wettability with respect to low surface tension liquids and surface free energy (xcex3s) as determined through critical surface tension (xcex3c) are increased. Instead of applying a modified polymer coating (i.e., a new film layer) to the surface of an original halopolymer material, the object is to provide for an oxyhalopolymer material in which the original starting bulk halopolymer is permanently modified at the molecular level by removal of some of the halogen atoms, so the carbon backbone has halogen, oxygen and hydrogen atoms covalently bonded thereto. In essence, the original halopolymer which is modified to form an oxyhalopolymer has a sufficient number of halogen atoms permanently substituted with both hydrogen atoms and oxygen or oxygen-containing groups like hydroxy functionality covalently bonded to the carbon backbone usually to a surface depth of about 10 to about 100 xc3x85 to increase the surface free energy (xcex3s) while the hydrophobic properties are substantially unchanged and non-fouling properties are maintained.
Another embodiment of the present invention is to provide for adhesive-oxyhalopolymer composites which comprise a halopolymer material, such as a film having a first and second side with at least the first side""s outer surface modified by substituting hydrogen and oxygen or oxygen-containing groups for at least a portion of the halogen atoms thereby providing an oxyhalopolymer film. The oxygen or oxygen-containing groups substituted on at least the first side of the oxyhalopolymer film are chemically bonded to an adhesive to form a composite structure. If only one side of the halopolymer film is modified, the surface of the modified side will bond to an adhesive while the other side will retain the surface properties of the original halopolymer film. If both sides of the halopolymer film are modified and only one side of the modified film is bonded to an adhesive, the other modified side retains its chemical reactivity almost indefinitely with little or no reorientation of the surface functionality groups. This also allows for extended shelf-life of the adhesive-oxyhalopolymer composites of the present invention. It also allows for a stable film which may be used sometime in the future when the film is wrapped or layered upon itself for protecting a surface because the modified side without the adhesive is still reactive, and therefore, can form covalent bonds with the adhesive coated side as soon as contacted therewith.
If both sides of the halopolymer are modified and subsequently bonded to an adhesive then the double-sided adhesive oxyhalopolymer film may be xe2x80x9csandwichedxe2x80x9d between two other materials. This application forms an internal protective barrier by employing the halopolymeric properties between two materials, such as between layers of wood panels for laminating wood composites, between underlayment and floor tiles, plywood roof sheeting and asphalt tile or providing a bonding surface between two incompatible materials, and in preparing protective films, appliquxc3xa9s, and specifically when used as paint replacement films. The oxyfluoropolymer-adhesive laminate sandwiched within a multilayer composite structure is also useful in providing strength, and/or performing as a structural barrier to water, gas or other chemical substances within the composite structure, e.g., carbon or fiberglass composites. Additionally, an adhesive-oxyhalopolymer composite of the present invention may bond to itself allowing for overlap of an adhesive-oxyhalopolymer film onto itself during application to a surface. This provides for better sealing with virtually no degradation of the adhesive seal on the overlapping edges of the film.
In the adhesive-oxyhalopolymer composites, including the appliquxc3xa9s used as paintless replacement films of the present invention up to 98 percent, and more specifically, from about 20 to about 85 percent of the surface halogen atoms of the oxyhalopolymer material are permanently substituted with hydrogen and oxygen and/or oxygen-containing groups of which from about 3 to about 30 percent of the substituted halogen atoms are replaced with oxygen and/or oxygen-containing groups and from about 70 to about 97 percent of the substituted halogen atoms are replaced with hydrogen atoms. The exact amount of hydrogen, halogen and oxygen or oxygen containing functional groups depends on several variables, such as the type of polymer, the thickness of the same and resident time of exposure to the plasma gas/vapor mixtures used in the present invention. It has been discovered that there is an optimal time of exposure to the plasma gas/vapor mixtures for each type of polymer to provide the optimal level of controlled modification of the surface of the polymer, depending on the type of material to be bonded. It has also been discovered that there appears to be a differing degree of maximum bonding depending on the specific polymeric type (i.e., mechanical properties and inherent polymer characteristics).
The halogens are replaced to depths from about 10 to about 200 xc3x85, and preferably from about 10 to 100 xc3x85. However, the morphological properties and bulk properties of the oxyhalogenated surface remains substantially unchanged over the starting bulk halopolymer material.
Another embodiment of the present invention provides for appliquxc3xa9s comprising oxyhalopolymer-adhesive composites, which may function as paint replacement (paintless system) films comprising a halopolymer material, such as a film having both first and second sides, wherein one or both sides are modified by substituting hydrogen and oxygen and/or oxygen-containing groups for at least a portion of the surface halogen atoms thereon. The reactive oxygen or oxygen-containing sites on the first side of the halopolymer film may be chemically bonded to an adhesive for improved peel strength, and optionally, the oxygen or oxygen-containing sites introduced on the second side of the halopolymer film can be covalently bonded to metals, and especially a transition metal. Generally, the invention contemplates the addition of metals as films, foils, mesh and in circuitry format applied either directly to the outer oxyfluoropolymeric surface, or within the adhesive system for imparting a permeation barrier to gas, water or other chemicals, as well as for protection from various electromagnetic environmental effects, such as lightning, shielding EMI (electromagnetic interference), sensor transduction characteristics in detection of biological, chemical, nuclear contamination or corrosion onset. Generally, transition metals for this invention are intended to include metals from Groups IIIa, IVa, Va, VIa, VIIa, VIIIa, Ib, IIb, IIIb and IVb of the Periodic Table. The oxyhalopolymer-adhesive composite films having covalently bonded transition metals may also provide surfaces with catalytic activity. They may be utilized as biocidal coatings, shielding coatings, absorbing coatings to absorb sound or radiation, and as a surface barrier which may block the transfer of gas and water vapor. Further, they may be securely bonded to other substrates by applying the adhesive side of the modified halopolymer to the substrate. As previously mentioned, the adhesive film composites also provide protection from environmental effects, including corrosion. One of the objects of this invention therefore is to providexe2x80x94specifically for a multifunctional oxyhalopolymer paint replacement films or appliquxc3xa9s which utilize an adhesive system which firstly, inhibits or eliminates entirely the corrosion of metals, and, secondly, promotes good adhesion of the oxyfluoropolymer to either a metallic or non-metallic surface or material.
Various classes of corrosion inhibitors are contemplated. Generally, they include amine based organics, inorganic phosphates, chromates, tins, zinc phosphates, phosphosilicates, and other phosphates of varying particle sizes. More specifically, the appliquxc3xa9 composites may be comprised of compositions, i.e., oxyhalopolymeric film and adhesive system modified by compounding with various corrosion inhibitors including certain aminophosphonic acids, aminophosphorous acids and/or their zirconium, bismuth and calcium salts, and salts thereof with certain amines.
Additionally, because some specialized adhesives form stronger bonds when applied to surfaces with metallic characteristics, the metallic characteristics of the second side of the adhesive oxyhalopolymer film may be used as a surface for chemically bonding an adhesive.
It is yet a further object of the present invention to provide for a method of making the previously described adhesive-oxyhalopolymer composite films and appliquxc3xa9s, the method which comprises providing a halopolymer material wherein at least a portion of halogen atoms are substituted with hydrogen and oxygen or oxygen-containing groups to form an oxyhalopolymer material and contacting the oxyhalopolymer material with an adhesive.
Specifically, adhesive-oxyhalopolymers film composites and appliquxc3xa9s of the invention may be prepared by the steps of:
a) modifying at least one surface of a halopolymer material by treating the surface with a radio frequency glow discharge gas/vapor mixture under vacuum to permanently substitute at least a portion of the surface halogen atoms with hydrogen and oxygen or oxygen-containing groups at the molecular level to provide a material with at least one oxyhalopolymer surface; and
b) contacting the oxyhalopolymer surface of step (a) with an adhesive.
Any adhesive may be used that bonds to the surface functionality groups of the modified halopolymer including but not limited to epoxy, fluorine based, aqueous based, solvent based, acrylic, polyester, heat sealable, pressure sensitive including rubber, acrylic, vinyl acetates and/or silicone, release coating and mixtures thereof. The gas/vapor mixtures may be selected from hydrogen, water, methanol or other oxygen containing liquids (i.e., formaldehyde), and preferably a hydrogen/methanol or hydrogen/water mixture.
The method imparts reactive sites that chemically bond to an adhesive. Plasma gas/vapor mixture concentrations of hydrogen, water, methanol, and other oxygen-containing liquids, such as formaldehyde together with wattage or power of the glow discharge and time of plasma treatment are variables which determine the depth of surface modifications at the molecular level, as well as the respective atomic concentrations of carbon, halogen, hydrogen and oxygen making up the oxyhalopolymer surface.
The invention further contemplates oxyhalopolymer-adhesive film composites for use as appliquxc3xa9s in which the original halopolymer material has from about 1 to about 100 percent of the surface halogen atoms to depths from about 10 to about 100 xc3x85 permanently substituted with hydrogen and oxygen or oxygen-containing groups of which from about 3 to about 100 percent of the oxygen or oxygen-containing groups are chemically bonded to an adhesive.
A further principal embodiment of the present invention provides for adhesive-oxyhalopolymer composites that are prepared from non-halogenated substrates, such as fibers, films and sheets, consisting of polymeric materials(non-halogenated), e.g., thermosetting and thermoplastic resins and plastics; ceramic materials; and/or metallic materials. The surface of the non-halogenated substrate is modified either by halogenation processes through bonding of halogen atoms to the polymer backbone, or by coating a halocarbon film thereto. The halogenated and halocarbon coated surfaces of the non-halogenated substrates are subsequently oxyhalogenated to provide reactive sites for chemically bonding with an adhesive to form the adhesive-oxyhalopolymers composites of the present invention.